1. Field of the Invention
The present invention relates to an interchangeable lens of a camera system. The camera system includes this interchangeable lens and a camera body to which the interchangeable lens is detachably attached. The present invention also relates to a method of performing data communications between the interchangeable lens and the camera body of the camera system.
2. Description of the Related Art
A conventional camera system is used by combining a camera body and an interchangeable lens selected from among various interchangeable lenses, and accordingly, each interchangeable lens incorporates a memory into which lens data inherent in the interchangeable lens is written so that the camera body reads out this lens data from the memory to use this lens data for controlling a photographic operation at a time of exposure. For instance, in conventional zoom lenses such as disclosed in U.S. Pat. No. 6,336,754 and Japanese Unexamined Patent Publication H11-231398, lens data is written into memory by a paging method for each focal length step because the lens data needs to be changed according to variations in focal length caused by a zooming operation. Upon the focal length of the zoom lens being changed, a page corresponding to the changed focal length is designated via hardware, and thereupon the camera body reads in all the data in this designated page.
In conventional SLR camera systems using an interchangeable zoom lens, the camera body can read in lens data quickly because a change in focal length of the zoom lens switches via hardware from the currently-selected page to a page corresponding to the changed focal length.
In recent years, in camera systems in which the camera body reads in lens data by carrying out communication with the interchangeable lens mounted to the camera body, it has been desired to enable a memory having an optimum memory capacity to be selected as a configuration in which a logic IC (gate array) serves as an interface on the interchangeable lens side and in which the memory is connected to the logic IC to enhance the degree of freedom in cost cutting and expansion of capability. Moreover, in this case also, it has been desired that the camera body can obtain lens data, which varies according to variations in focal length caused by a zooming operation or variations in object distance (photographing distance) caused by a focus adjusting operation, quickly without the need for the camera body to take the focal length and the object distance of the interchangeable lens into consideration. Furthermore, it has been desired that new exchange lenses having a larger amount of memory maintain compatibility with prior-art SLR camera bodies and camera systems.